Central nervous system toxicity is a recognized side effect of certain therapies for cancers, particularly cranial irradiation, intrathecal therapy or systemic high-dose chemotherapy. The pathophysiologic mechanisms and clinical manifestations vary. Previous studies defining MRI changes and correlating these with neurocognitive deficiencies have been inconsistent. Recent advances in brain imaging may help to better define neurotoxic effects. 1H-NMRS is a noninvasive method of obtaining in vivo biochemical information from the brain. It has been used to study patients with CNS disorders, including neuronal disorders. In this study, 1H-NMRS will be used to objectively characterize CNS toxicities in patients with cancer who are receiving potentially neurotoxic therapies. In addition, we will retrospectively evaluate patients with known or suspected neurotoxicity associated with cancer therapy, to determine if changes in spectroscopic patterns are associated with CNS toxicity.